Collective evidence from several disciplines of study indicates that tooth pulp afferents transmit both nociceptive and non-nociceptive information to the central nervous system. The latter may be subserved by intradental mechanoreceptors. The general goals of this study in cats are 1) to elucidate the physiological properties of intradental mechanoreceptors and related brain stem neurons by means of calibrated stimuli and 2) to identify the location and structure of these mechanoreceptors within the tooth and the location of their axon terminals in the brain stem. We will test the hypothesis that 1) intradental mechanoreceptors are functionally different than mechanoreceptors in periodontal ligaments (PDL) and nociceptors within teeth and 2) intradental mechanoreception is principally represented in the central nervous system by trigeminal "lemniscal type" neurons. The first objective is to examine the dynamic behavior of the tooth when subjected to sinusoidal vibration. Tooth mechanical impedance curves will be compared to the discharge tuning-threshold curves of mechanoreceptors in the tooth and PDL and of related brain stem neurons. The second objective is to compare the response properties of intradental mechanoreceptors with those of intradental nociceptors and PDL mechanoreceptors. Quantifiable thermal and mechanical stimuli will be applied to the enamel surface of the intact tooth. The resultant acceleration, force and velocity of applied mechanical stimulation, tooth displacement and dentinal temperature will be monitored. The third objective is to iontophoretically inject axonal tracing agents into the cell bodies of functionally characterized, intradental receptors to allow mapping of terminal axon arbors in the tooth and brain stem trigeminal nuclei. The final objective is to determine by recording brain stem evoked potentials which trigeminal nuclei receive input from intradental mechanoreceptors and to determine by extracellular recording the extent to which low and high threshold input from other orofacial sites converge onto brain stem neurons that receive intradental mechanoreceptive input. The long-term objectives of these studies are to improve our understanding of the physiology and anatomy of dental innervation and trigeminal neural mechanisms in the brain stem. Findings from these studies will contribute to formulation of new strategies to alleviate dental orofacial pain.